As the first week of the government shutdown winds down Friday, government employees are on edge about when they'll get paid. Some 800,000 of them are furloughed, unsure of whether they'll eventually be paid for their time off.

But even more federal employees who are deemed too essential to be furloughed — including more than three-quarters of the NWS staff, its union chief told Popular Science — are still working, though they too could go without pay.

"There's no money to pay them," said Dan Sobien, the National Weather Service Employees Organization's president. "Nobody knows when anyone's going to get paid."